Preparation: Bring a large pot of water to a boil. Add salt and the pasta and cook until al dente. While the pasta is cooking, remove 1/4 to 1/2 cup of the pasta cooking water and set it aside. Drain the pasta quickly in a colander. Be careful not to overcook. Quickly put the drained pot back onto the burner over medium heat. Working quickly, return the pasta to the pot. Add the reserved 1/4 cup cooking water (or more if the mixture seems too dry), Gruyere and butter. Cook over medium heat, stirring constantly, until the cheese and butter are melted. Remove from the heat and stir in the walnuts . Add salt and pepper to taste. Serve in warm bowls with additional salt and pepper and a bit of grated Parmigiano-Reggiano atop each bowl. Yield: 4 servings Per Serving: Calories 643 (45% fat), Fat 32 g (13 g saturated), Fiber 3 g, Cholesterol 143 mg, Sodium 219 mg, Carbohydrates 63 g, Calcium 472 mg. Recipe Source: Zingerman's Guide to Good Eating: How to Choose the Best Bread, Cheeses, Olive Oil, Pasta, Chocolate, and Much More by Ari Weinzweig, Zingermans Restaurant (Houghton Mifflin) Reprinted with permission.